Method and apparatus for treating surface of semiconductor

ABSTRACT

According to the present invention, there is provided a sample surface treating apparatus for processing a fine pattern by plasma etching, comprising: a stage provided in a chamber, on which a sample to be subjected to a surface treatment is placed; etching gas supplying means for continuously supplying an etching gas for plasma generation into the chamber; plasma generating means for generating a high-density plasma in the chamber; a bias power supply for applying a bias voltage of 100 kHz or higher to the stage independently of the plasma generation; and pulse modulating means for modulating the bias power supply at a frequency of 100 Hz to 10 kHz, wherein a surface treatment in which the minimum feature size is 1 μm or smaller is performed to the sample placed on the stand.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to method and apparatus for treating the surface of a semiconductor and, more particularly, to surface treating method and apparatus adapted to etching of the surface of a semiconductor by using a plasma.

[0003] 2. Related Background Art

[0004] Hitherto, as a means for treating the surface of a semiconductor, a plasma etcher for etching a semiconductor in a plasma is known. Conventional techniques will be described by using an etcher called an ECR (electron cyclotron resonance) etcher as an example. According to the ECR etcher, a plasma is generated by microwaves within a chamber to which a magnetic field is applied from the outside. The motion of electrons is circular around the magnetic field, and high density plasma is produced by resonance of electron motion and microwave. In order to accelerate ions impinging on a sample such as a semiconductor, a high frequency voltage is applied to the sample. A halogen gas formed from chlorine, fluorine, or the like is used as a plasma gas.

[0005] Among conventional etchers of such a kind, an etcher for realizing high accuracy of processing disclosed in Publication of Unexamined Japanese Patent Application (JP-A) No. 6-151360 (corresponding to U.S. Pat. No. 5,352,324) is known. According to the invention, by on-off modulating a high frequency voltage to be applied to the sample, the selectivity between silicon (Si) serving as a substance to be etched and an underlying oxide film can be increased and the aspect ratio dependence can be reduced. JP-A-8-339989 (corresponding to U.S. Pat. No. 5,614,060) discloses a method which can reduce etch residue by overlapping short pulses of a continuous rf bias power in etching performed to a metal. JP-A-62-154734 discloses a method of processing a taper by introducing a gas bringing about deposition and etching and alternately applying a DC bias higher than a predetermined potential and a DC bias lower than the predetermined potential. JP-A-60-50923 (corresponding to U.S. Pat. No. 4,579,623) discloses a method of improving the surface treating characteristics by periodically varying an introducing amount of etching gas and also changing application time of the high frequency voltage. Examined Japanese Patent Application Publication No. 4-69415 (corresponding to U.S. Pat. No. 4,808,258) discloses a method of improving the etch characteristic by modulating the high frequency voltage to be applied to a sample. Further, U.S. Pat. No. 4,585,516 discloses a method of improving uniformity in the etch rate in the plate of a wafer by modulating the high frequency voltage of at least one of high frequency power supplies connected to two electrodes in a triode etcher.

[0006] As a semiconductor becomes finer, a processing dimension between a line corresponding to a conductive line or an electrode and a space enters a region of 1 μm or smaller, preferably, 0.5 μm or smaller. In the processing of such a fine pattern, a problem such that lines gradually become thicker and a pattern cannot be formed according to a design dimension is conspicuous. Further, in addition to an aspect ratio dependent etch rate, an aspect ratio dependent etch profile becomes conspicuous, thereby hindering the processing.

[0007] Moreover, the thickness of a gate oxide film of a MOS (metal oxide semiconductor) transistor is equal to or smaller than 6 nm in 256 Mbit or lager LSI (Large Scale Integration). In such devices, the degree of anisotropy and the selectivity between a material to be etched and the underlying oxide film have the relation of trade-off, so that the processing is made more difficult.

[0008] Many of the conventional techniques were invented when the minimum feature size of a device was 1 μm or larger. It is becoming difficult for the techniques to process a finer device. In processing such a fine device, it is necessary to organize accurate process parameters based on analysis of the relation between plasma parameters and etch characteristics. At present, many manufactures spare much efforts on this organization. By the organized process, a new device which is qualitatively different can be also processed.

SUMMARY OF THE INVENTION

[0009] It is an object of the invention to provide method and apparatus for treating the surface of a semiconductor, which can process a device whose processing dimension is 1 μm or smaller, preferably, 0.5 μm or smaller so as to respond to the needs for finer semiconductor.

[0010] A feature of the invention relates to a surface treating apparatus comprising: a stage provided in a chamber, on which a sample to be subjected to a surface treatment is placed; etching gas supplying means for continuously supplying an etching gas for plasma generation into the chamber; plasma generating means for generating a high density plasma in the chamber; a bias power supply for applying a bias voltage of 100 kHz or higher frequency to the stage independently of the plasma generation; and pulse modulating method for modulating the bias power supply with a frequency of 100 HZ to 10 kHz, wherein a surface treatment in which the minimum feature size is 1 μm or smaller is performed to the sample placed on the stage.

[0011] Another feature of the invention relates to a sample surface treating method of applying a radio frequency (rf) bias to the sample and time-modulating the rf bias when a sample having a gate electrode on SiO₂ serving as an underlying film whose thickness is 6 nm or smaller is etched by using a plasma.

[0012] Another feature of the invention relates to a method of treating the surface of a sample by continuously supplying an etching gas into a chamber, generating a high density plasma in the chamber, and applying an rf bias voltage to the stage independently of the plasma generation, wherein a surface treatment in which the minimum feature size is 1 μm or smaller is performed to the sample placed on the stage by using a mixed gas of chlorine and oxygen as the etching gas, and on-off modulating the bias power supply.

[0013] According to the invention, in a processing of a fine pattern, an rf voltage to be applied to a sample is on-off modulated and a combination of a frequency of the rf voltage and the on-off frequency is devised, thereby increasing the degree of anisotropy of etching and also increasing the etch selectivity. Thus, the process of a device whose processing size is 1 μm or smaller, preferably, 0.5 μm or smaller can be realized. Specifically, by the narrow band of an ion energy distribution, the trade-off between the anisotropy and the selectivity as a problem in processing a fine device is solved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a block diagram showing a whole etcher according to an embodiment of the invention;

[0015]FIG. 2 is a flowchart showing the operation at the time of etching by the etcher of FIG. 1;

[0016]FIG. 3 is a diagram showing the relation between an rf bias frequency and an on off frequency in the etcher of FIG. 1;

[0017]FIG. 4 is a diagram showing an ion energy distribution;

[0018]FIG. 5 is a cross section of a sample treated by applying the invention;

[0019]FIG. 6 is a cross section of a sample at the time of treatment in a comparative example;

[0020]FIG. 7 is a cross section of a sample at the time of treatment in a comparative example;

[0021]FIG. 8 is a diagram showing the relation between a polysilicon etch rate and selectivity;

[0022]FIG. 9 is a diagram showing the relation between an amplitude of an rf bias voltage and the depth of a microtrench;

[0023]FIG. 10 is a diagram showing the relation between the thickness of a gate oxide film and the permissible depth of a microtrench;

[0024]FIG. 11 is a cross section of a sample at the time of etching;

[0025]FIG. 12 is a cross section of a sample at the time of treatment to which the invention is applied;

[0026]FIG. 13 is a cross section of a sample at the time of treatment in a comparative example;

[0027]FIG. 14 is a cross section of a sample at the time of treatment to which the invention is applied;

[0028]FIG. 15 is a cross section of a sample at the time of treatment in a comparative example;

[0029]FIG. 16 is a block diagram of a whole etcher according to another embodiment;

[0030]FIG. 17 is a block diagram of a whole etcher according to another embodiment;

[0031]FIG. 18 is a cross section of a sample at the time of treatment to which another embodiment of the invention is applied;

[0032]FIG. 19 is an enlarged diagram of a stage in an etcher according to another embodiment of the invention; and

[0033]FIG. 20 is a block diagram of a whole etcher according to another embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] Embodiments of the present invention will be described hereinbelow with reference to the drawings. A first embodiment of the invention will be described first with reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing a whole plasma etcher to which the invention is applied. Microwaves are introduced from a magnetron 101 via an automatic matching apparatus 106, a waveguide 102, and a transparent window 103 into a chamber 104. Meanwhile, an etching gas such as halogen gas is introduced into the chamber 104 via a gas introducing means 100 and a plasma of the gas is generated in association with the introduction of the microwaves. The transparent window 103 is made of a material such as quartz and ceramics which transmit microwaves (electromagnetic waves).

[0035] Around the chamber 104, coils 105 are arranged. The magnetic flux density of the coils 105 is set so as to resonate with the frequency of the microwaves. For example, when the frequency is 2.45 GHz, the magnetic flux density is 875 Gauss. With the magnetic flux density, the cyclotron motion of electrons in the plasma resonates with the frequency of the electromagnetic waves, so that the energy of the microwaves is efficiently supplied to the plasma. Thus, a high density plasma can be produced.

[0036] A sample 107 is placed on a stage 108. In order to accelerate ions impinging on the sample 107, an rf (radio frequency) bias power supply 109 serving as an rf power supply is connected to the stage 108 via a high-pass filter 111. An insulating film 110 such as a ceramic or polymer film is formed on the surface of the stage 108. A DC power supply 112 is also connected via a low-pass filter 113 and a voltage is applied to the stage 108, thereby holding the sample on the stage by the electrostatic chuck.

[0037]FIG. 2 shows the gas supply in the chamber 104 and the operations of the magnetron 101 and the rf bias power supply 109 at the time of etching by the etcher of FIG. 1. As shown in (a), a gas is supplied and the gas pressure is kept constant upon start of the etching. As shown in (b), the microwave power is also continuously supplied. On the other hand, as shown in (c), the rf bias applied to the sample is periodically on-off modulated. By generating ion accelerating periods and un-accelerated periods by the on-off modulation of the rf bias, periods in which ion energy is high and periods in which the ion energy is low are produced during the time of the sample surface treatment. As shown in (d), in the low energy ion period, the etching does not develop. Rather, reaction products in the gas or plasma are deposited.

[0038] The relation among the frequency of the rf bias, the on-off frequency, and the etch characteristic will now be described. FIG. 3 shows waveforms of the rf biases. (a) corresponds to the etch parameters of the present embodiment and shows a waveform when the rf bias frequency is 100 kHz and the on-off frequency (modulating frequency) is 100 Hz. (b) shows a waveform when the rf bias frequency is 1 kHz and the on-off frequency (modulating frequency) is 1 Hz as known from the publication of Unexamined Japanese Patent Application No. 6-151360 (corresponding to U.S. Pat. No. 5,352,324).

[0039] When the rf bias is applied to the stage, a region (called a “sheath”) of a high electric field is produced in the region of almost 1 mm or smaller in the thickness direction from the surface of the sample, and ions are accelerated in the sheath. A distribution of the energy of the accelerated ions depends on the rf bias frequency. When the rf bias frequency is sufficiently low, the motion of ions follows a change in the voltage expressed by a sinwave, so that the ions have the same energy as an instantaneous value Vx (FIG. 3(b)) of the voltage. The energy distribution becomes very wide as shown by the chart of 1 kHz in FIG. 4.

[0040] When the frequency of the rf bias becomes high, the motion of ions cannot follow the fluctuation in the rf bias. Consequently, the energy of ions gradually converges on the value of a DC component Vdc of a voltage generated at the time of application of the rf bias. There is a transient state during the period. When the frequency lies in a range from about 100 kHz to few MHz, as shown by the chart of 100 kHz in FIG. 4, the energy of ions has a saddle-shaped distribution including a peak 401 of high energy corresponding to the peak to peak amplitude Vpp of the rf bias and a peak 402 of low energy. The peak 402 of the low energy corresponds to ions which enter the sheath when the rf bias is 0W, that is, just at a timing when the ions are not accelerated due to a fluctuation in the rf bias. The ions are not accelerated in the period during which the rf bias is off, and all of the ions enter a region corresponding to the low energy peak 402 in FIG. 4.

[0041]FIG. 5 shows the result of a case where a fine pattern comprising lines and spaces is etched on the surface of a sample by using the etcher of FIG. 1. A mixed gas of chlorine (72 sccm) and oxygen (8 sccm) was used as an etching gas, and the pressure in the chamber 104 was set to 0.4 Pa. The microwave output from the magnetron 101 was set to 400W. The structure of the etched semiconductor is as follows. The thickness of a gate oxide film 502 on a silicon substrate 501 is 4 nm, the thickness of a polysilicon film 503 is 300 nm, the thickness of a resist 504 is 1 μm, the width of each line is 0.4 μm, and the width of each space is 0.4 μm. FIG. 5 shows an etch profile when the frequency of the bias power supply 109 was set to 100 kHz and the on-off frequency was set to 100 Hz. The peak output of the rf bias was 300W and the duty ratio (the ratio of the on periods in a certain cycle) was 20%.

[0042]FIG. 6 shows an etch profile as a comparative example in which the frequency of a bias power supply which is known from the Examined Japanese Patent Application Publication 6-151360 (corresponding to U.S. Pat. No. 5,352,324) was set to 1 kHz and the on-off frequency was set to 1 Hz. The peak output of the rf bias was 300W and the duty ratio was 20%.

[0043]FIG. 7 is a cross section of a comparative example when the rf bias frequency was set to 100 kHz and a continuous output power was set to 60W. With the parameters, the etch rate of the polysilicon film 503 was approximately 250 nm/min. and the selectivity between the polysilicon film and the oxide film was about 20.

[0044] FIGS. 5 to 7 show the profiles during the etching of the polysilicon film 503. By the etching (FIG. 5) according to the method of the invention, vertical sidewalls and flatly etched bottom surface are obtained. There is no aspect ratio dependence, so that the etch depth of a wide part 506 and that of a narrow space part 505 are equal.

[0045] On the other hand, in case of performing the etching with the continuous wave bias (FIG. 7) shown as a comparative example, the sidewalls are not so vertical. With respect to a sidewall 507 facing a narrow part and a sidewall 508 facing a wide part, the verticality of the latter is worse. A fine trench 509 called a microtrench is formed on the etched bottom surface. Further, the aspect ratio dependence occurs, and the difference D in the etch depth occurs between the narrow part and the wide part.

[0046] Even if the rf bias is on-off modulated, when the rf bias frequency is low (FIG. 6) shown as a comparative example, although the verticality of the sidewalls is higher than that of the case using the continuous wave bias, undercutting occurs in the resist 504. The verticality is lower than that of the case of FIG. 5 to which the method of the present invention is applied.

[0047] The causes of the above results will be mentioned. In comparison between the on-off modulation of the rf bias (on-off bias or time modulation bias) and the continuous application (continuous wave bias), since the energy of ions for obtaining the same polysilicon etch rate can be set higher by on-off modulating the rf bias, the degree of anisotropy can be improved. For example, the amplitude Vpp when the continuous wave bias is 60W is 320V and the amplitude Vpp when the on-off bias peak power is 300W is 1,410V. The energy of the ions is almost proportional to the amplitude Vpp of the bias voltage. Consequently, since the energy of the ions can be increased by the on-off bias as compared with the continuous wave bias, the verticality is improved.

[0048] On the other hand, even if the continuous wave bias is used, by increasing the amplitude Vpp, the verticality is improved. However, the etch rate of the oxide film becomes higher almost in proportional to the amplitude Vpp, so that the selectivity between the polysilicon film and the oxide film becomes low. The etching becomes therefore unsuitable for a case where the underlying oxide film is thin such as etching of a gate electrode in a transistor.

[0049] That is, regarding the on-off bias, by providing off periods in the acceleration of ions, the number of high energy ions is reduced, so that the verticality can be raised without deteriorating the selectivity. The microtrench is formed when the verticality of the sidewalls becomes lower, ions are reflected from the sidewalls and the bottom surface is bombarded with the ions. When the verticality of the sidewalls is improved, the microtrench is therefore also reduced and a flatly etched bottom surface can be obtained.

[0050] Even when the rf bias is on-off modulated, if the rf bias frequency is low, a number of ions having an intermediate energy exist as shown in FIG. 4. Consequently, undercutting occurs. To be more specific, the etch reaction is promoted by the impinging of the ions having the energy of a threshold or more. Although ions having the intermediate energy promote the etching reaction, since the energy is low, their directionality is bad. Consequently, the ions impinge on the polysilicon sidewall 503 under the resist 504, thereby causing the undercut.

[0051] By setting the rf bias to 100 kHz or higher as in the embodiment, the ions having the intermediate energy can be reduced, so that highly anisotropic etching can be realized. More specifically, in order to raise the degree of anisotropy of the etching, it is necessary to set the energy of ions so as to have a distribution including high and low peak points. Low ion energy does not contribute to etching and high ion energy has the high directionality. Effects of the on-off modulation of the rf bias prove the real worth for the first time when the rf bias is set to 100 kHz or higher at which the ion energy has the distribution including the high and low peak points.

[0052] A second embodiment of the invention will be described. The duty ratio of the on-off rf bias and the ion energy will be first described. FIG. 8 shows the relation between the etch rate of polysilicon and the etch selectivity between the oxide film and the polysilicon film, and the case using the continuous wave bias and the case using the on-off bias are compared with each other. In the example, the output of microwaves from the magnetron 101 was set to 400W, the output of the bias power supply 109 was set to 60W, the frequency was set to 800 kHz, the on-off frequency was set to 1 kHz, the gas was made from chlorine (185 sccm) and oxygen (15 sccm), and the pressure was 0.8 Pa. Although the rf bias power is a parameter, in the on-off bias modulation, the power was controlled by setting the peak power to 60W and varying the duty ratio. To be specific, when the duty ratio is 50%, the power is 30W (50% of 60W).

[0053] As understood from FIG. 8, with respect to the on-off bias modulation, the selectivity increases in a region where the duty ratio is 50% or lower as compared with the continuous wave bias. Even if the ion energy is increased, the degree of anisotropy can be therefore increased without decreasing the etch selectivity. The lower the duty ratio is, the larger the effects are. When the duty ratio is too low, however, the polysilicon etch rate becomes low. In practice, consequently, it is preferable to set the duty ratio within a range from 5% to 50%.

[0054] The reason why the above-described effects can be obtained by the on-off modulation of the rf bias, that is, time modulation will be described hereinbelow.

[0055] It is considered that the reason why the selectivity is increased by the on-off bias modulation is that the reaction products are deposited on the oxide film during the off period of the rf bias, thereby reducing the etch rate of the oxide film. Especially, the reaction products of chlorine, oxygen, and silicon tend to be deposited on the oxide film in the region where the temperature is low. Since the energy of ions impinging on the surface of the sample is low during the rf bias off period, the surface temperature becomes also low. The reaction products are deposited on the oxide film during the off period, and the selectivity is higher as compared with that of the continuous wave bias at the same Vpp and that of the continuous wave bias with the parameter of Vpp at which the same etch rate can be obtained. In the on-off bias modulation as well, when the ion energy is made higher than the amplitudes Vpp of continuous bias case, the etch rate of the oxide film increases and the same selectivity as that in the case of using the continuous wave bias is obtained. Since the ion energy is high in the region, however, as shown in the embodiment of FIG. 5, the highly anisotropic etch without any microtrench can be realized. Generally, the higher the ion energy is, the more the aspect ratio dependence is reduced. Consequently, by the on-off bias modulation, the aspect ratio dependence can be also reduced without decreasing the selectivity.

[0056] Parameters of the ion energy to increase the degree of anisotropy and reduce the microtrench will now be described. FIG. 9 shows the relation between the rf bias voltage and the depth of the microtrench which were obtained by experiments. In this case, the depth of the microtrench denotes the depth of the fine trench 509 formed on the trench bottom of polysilicon expressed by “L” in FIG. 7. The depth of the microtrench permitted by the process of a gate of a transistor will be obtained hereinbelow. In the process of the gate, it is necessary to perform the etching so that there is no etch residue of polysilicon on the bottom of the trench while the gate oxide film 502 is sufficiently left. In a thin region where the thickness of the gate oxide film is 6 nm or smaller, the thickness of the gate oxide film after the etching has to be 2 nm or larger. If the polysilicon film corresponding to the depth L of the microtrench cannot be etched within a time the thickness of the gate oxide film becomes 2 nm or larger, the etch residue of polysilicon occurs on the trench bottom.

[0057] When an amount of the polysilicon which can be etched until the remaining of the gate oxide film becomes 2 nm is set to a permissible microtrench depth Lmax(nm), Lmax=S(d−2), where S denotes the selectivity between polysilicon and the oxide film and d(nm) indicates the initial film thickness of the gate oxide film. The relation is shown in FIG. 10.

[0058] Further, etch profiles at points A, B, and C in FIG. 9 are shown in FIG. 11. From the FIGS. 9 to 11, the ion energy which can satisfy both the anisotropy and the gate oxide film residue amount is obtained. First, with respect to the verticality of the etched sidewall, when the amplitude Vpp is 500V or higher, the verticality reaches a sufficient level in a device having the minimum feature size of 1 μm to 0.1 μm. When Vpp is 500V to 1000V, in the above-described etching using the continuous wave bias of chlorine and oxygen, the etch selectivity lies within a range from 10 to 5.

[0059] It will be understood from FIG. 10 that, for example, in case of processing the gate oxide film of 6 nm, the permissible microtrench depth at the etch selectivity of 5 is about 20 nm. It will be understood from FIG. 9 that the process can be performed from a calculation viewpoint when Vpp is set to 500V or higher since the microtrench depth becomes 20 nm or smaller in a region where Vpp is 500V or higher. When the selectivity is 10 or lower, however, if the etching is not stopped accurately at the endpoint of the etching, the gate oxide film is etched because there is no allowance. A method of increasing the selectivity while maintaining Vpp at 500V is therefore required, that is, the cooperation of the on-off bias is necessary.

[0060] A physical quantity which directly exerts an influence on the depth of the microtrench and the selectivity does not relate to the amplitude Vpp but the ion energy. Since it is difficult to measure the ion energy in practice, the amplitude Vpp is used as an index of the ion energy. The relation between the ion energy and the rf voltage will now be described. When the rf voltage is applied to the stage via a plasma, a DC potential (hereinbelow, referred to as “Vdc”) is so generated as to attract ions into the stage by the action for flowing a current between the earth (generally, a conductive wall serves as the earth) and the electrode. The ions are accelerated by an electric field obtained by overlapping Vdc and the rf voltage which changes with time. The maximum ion energy which can be obtained varies depending on whether the motion of ions follow the change with time of the rf voltage. Generally, the density of a plasma used for etching is equal to or higher than 1×10¹⁰/cm⁻³. With the density, the ions travel through the plasma sheath and reach the sample during the period in which the rf voltage is negative, that is, during a period of ½ of sinewave when the rf bias frequency is 15 MHz or lower. Emax is therefore almost equal to a value obtained by adding Vdc to the value of ½ of the voltage amplitude (Vpp/2). In reality, there is a voltage drop or the like in an electric circuit. It is known from measurement that Emax is 400 eV when Vpp is 500V. Since a substantial physical quantity which exerts an influence on the etch profile is not Vpp but the ion energy, in order to obtain a profile without any microtrench, it is sufficient to set the maximum value of the ion energy to 400 eV or higher. When the frequency of the rf bias increases and the motion of ions does not follow the change in voltage, Emax gradually approaches Vdc. A period during which the frequency is from 15 MHz to few tens MHz is a transient period. In such a case as well, if Vpp is set to 800V or higher, Emax sufficiently becomes 400 eV or higher.

[0061] Although the required amplitude Vpp varies according to the structure of a device and the etching gas, the amplitude of 500V or higher is a reference. When the underlying film is thick and occurrence of the microtrench does not exert any influence or, as will be described hereinlater, when the etching is divided into some steps and the invention is applied to an over etch after completion of a main etch, the amplitude Vpp can be set to a lower value. In this case, about 100V is sufficient.

[0062] A third embodiment in which the invention is applied to etching performed to another material and the result will be described. As shown in FIG. 12, a sample is formed in such a manner that 4 nm of an oxide film 502 is deposited on a silicon substrate 501, 300 nm of a polysilicon film 503, 80 nm of tungsten silicide (WSi) film 1201, and an uppermost layer of a silicon nitride film 1202 patterned as a mask are sequentially deposited. As an etching gas, a mixed gas of chlorine (185 sccm) and oxygen (15 sccm) was used. The pressure of the etching gas was set to 0.8 Pa. An output of the microwave from the magnetron 101 was set to 400W. The frequency of the rf bias power supply 109 was set to 800 kHz.

[0063]FIG. 13 shows an etch profile of a comparative example in which the continuous wave bias was set to 60W. FIG. 12 shows an etch profile when the peak output of the on-off bias was set to 300W and the duty ratio was set to 20%. In the samples as well, when etching was performed with the continuous wave bias, the verticality is low and the aspect ratio dependency is large. On the other hand, according to the on-off bias method of the invention, the verticality of sidewalls is improved. Further, in the sample, whiskers 1203 are shown on the etched surface of polysilicon. It is assumed that the whiskers 1203 are formed due to a micro mask on the interface between the polysilicon film 503 and the WSi film 1201. The whiskers 1203 cause the etch residue. The on-off bias method can reduce the density of the whiskers as well.

[0064] A fourth embodiment in which the invention is applied to etching performed to a metal such as aluminium and its result will be described. The structure of a sample is as shown in FIG. 14. 300 nm of an oxide film 1401, 100 nm of a TiN film 1402, 400 nm of Al film 1403, and 75 nm of a TiN film 1404 are sequentially deposited on the Si substrate 501. 1 μm of a resist mask 504 is formed as an uppermost layer. The dimension of each of a line and a space was 0.4 μm. As the etching gas, a mixed gas of chlorine (80 sccm) and BCl₃ (20 sccm) was used and the pressure was set to 1 Pa. An output of the microwave power supply 101 was set to 700W, a stage temperature was set to 40° C., the frequency of the rf bias power supply 109 was set to 400 kHz, and the on-off frequency was set to 2 kHz.

[0065]FIG. 14 shows an etch profile when the peak power of the on-off bias modulation was 350W and the duty ratio was 20%. FIG. 15 shows an etch profile of a comparative example when the power of the continuous wave bias was set to 70W. With the values of the powers, the etch rates of aluminium are substantially equal. In the sample shown in FIG. 15, the aspect ratio dependency is large, and the verticality of the sidewall 1405 facing a wider space when the continuous wave bias is used especially deteriorates. The aspect ratio dependence is, however, suppressed by using the on-off bias modulation. That is, in case of the metal as well, the higher the ion energy is, the more the degree of anisotropy or the aspect ratio dependence is improved. Since the ion energy can be set to be high without decreasing the selectivity between the metal and the underlying oxide film by using the on-off bias modulation, the above effects are produced.

[0066] As a method of further utilizing the effects of the invention, there is a method of dividing the etch process into a plurality of steps. The method will be described as a fifth embodiment. FIG. 16 shows a change with time in the etch profile when a sample as a substance to be treated is processed in steps. A sample is formed in such a manner that 4 nm of an oxide film 502 is deposited on a silicon substrate 501, 200 nm of polysilicon 503 and 200 nm of a silicon nitride film 1801 are sequentially deposited. The silicon nitride film is processed in a desired pattern. The interval between a line and a space is 250 nm. A native oxide film 1802 is usually formed on the surface of the polysilicon 503.

[0067] The sample having the structure is etched in three steps. FIG. 16(a) illustrates an initial state. In step 1, the native oxide film 1802 is eliminated. Cl₂ (200 sccm) was used as an etching gas and the pressure was set to 0.8 Pa. The output of the microwave power supply 101 was set to 400W. The frequency of the rf bias power supply 109 was 800 kHz. Since the step 1 aims at eliminating the thin native oxide film, time was set to five seconds and the continuous output of the rf power supply 109 was set to 60W. The profile of the sample after completion of step 1 is shown in FIG. 16(b).

[0068] Step 2 relates to etching of the polysilicon 503 as a main part of the process. The etching will be referred to as a “main etch” hereinbelow. Since the profile control in this step is the most important, the rf bias power supply 109 is on-off modulated in step 2, the power was set to 200W and the duty ratio was set to 30%. The amplitude Vpp was 1000V. As an etching gas, a mixed gas of chlorine (185 sccm) and oxygen (15 sccm) was used and the pressure was set to 0.8 Pa. The other parameters were the same as those in step 1. With the parameters, the etch rate of the polysilicon was 300 nm/min. and the selectivity of the polysilicon and the oxide film was 20. The etching time was set to 35 seconds. The profile after completion of step 2 is shown in FIG. 16(c). Side faces perpendicular to the flat bottom surface without any microtrench can be obtained. The time in step 2 was set so as to leave a small amount of the polysilicon 503 remains.

[0069] In the last step 3, since the thin underlying oxide film 502 is exposed, the parameters are changed so that the selectivity is high even if the etch rate of the polysilicon is lowered. Specifically, the continuous power of the rf bias power supply 109 was set to 30W. The other parameters were the same as those in step 2. With the parameters, the etch rate of the polysilicon becomes 100 nm/min. and the selectivity is 50. Etching having a relatively high selectivity after completion of the main etch is called an over etch. The etch time was set to 30 seconds. The profile after completion of step 3 is shown in FIG. 16(d). By raising the selectivity, the process can be performed while the underlying oxide film is sufficiently left without etch residue of the polysilicon 503. Although the continuous wave bias was used in step 3, the peak power can be reduced in the on-off bias modulation.

[0070] As described above, by applying the on-off bias modulation to the process of the main part of the sample as a substance to be etched, a desired processing can be performed without damaging the very thin underlying film.

[0071] Even if a substance to be etched has a multilayer structure of various substances, a high-precision process causing no shape deformation can be carried out by increasing the number of steps. To which step the on-off bias modulation is applied will be properly determined according to the device structure. Parameters having a wider process margin can be set by using the on-off bias modulation. Although the etching gas is continuously supplied in the embodiment, when the etching is divided into some steps, the supply of the gas does not have to be continuous among the steps.

[0072] The structures of etchers to which the invention can be applied will be described. Since the invention aims to process a device whose minimum feature size is 1 μm, preferably, 0.5 μm or smaller, the effects are displayed when the invention is applied to a kind of a machine of a so-called high-density type in which the plasma electron density is 1×10¹⁰/cm⁻³ or higher, preferably, 1×10¹¹/cm⁻³ or higher. As etchers of this type, there are an inductively coupled plasma etcher and an ECR etcher. A capacitively coupled plasma etcher which has been known for long time has problems as described below and is not adapted to the invention. Since the etcher cannot generate a high density plasma, the throughput is low. As the plasma density is low, the sheath becomes thick and the ions are scattered in the sheath, thereby deteriorating the degree of anisotropy. Since the plasma cannot be generated in a region where the gas pressure is low, the ions scatter considerably.

[0073]FIG. 17 shows an inductively coupled plasma etcher as a sixth embodiment of the invention. The etcher generates a plasma by inductive coupling using the electromagnetic waves having a so-called rf frequency of few hundreds kHz to tens MHz. The chamber 104 is made of a substance such as alumina or quartz which transmits electromagnetic waves. A coil antenna 201 for generating a plasma is wound around the chamber 104. An rf power supply 203 is connected to the coil antenna 201. In the chamber, a stage 108 is provided, a sample 107 is placed on the stage 108, and an rf bias power supply 109 is connected. The chamber 104 has an upper lid 207. The chamber 104 and the upper lid 207 can be also formed integrally.

[0074] In the etcher of this kind as well, in a manner similar to the foregoing embodiments, the above-mentioned effects can be produced by on-off modulating the rf bias power supply 109. In the etcher shown in FIG. 17, when the coil antenna 201 is mounted on the upper lid 207, the same effects can be produced.

[0075] Further, as a seventh embodiment of the invention, an etcher having the structure for producing electron cyclotron resonance (ECR) between the electromagnetic wave and the magnetic field will be described with reference to FIG. 18.

[0076] Coils 105 are arranged around a chamber 104 having a gas introducing means 100. A plasma is obtained from a gas introduced into the chamber 104 by a mutual action of the electromagnetic waves introduced to an antenna plate 205 through a coaxial cable 204 and the magnetic field generated by the coils 105. A sample 107 is treated with the plasma. The sample 107 is placed on a stage 108 and is supported by electrostatic chucking. An rf bias for attracting ions to the sample 107 is applied from an rf bias power supply 109 via a matching apparatus 111 to the stage 108. A voltage for electrostatic chucking is applied from a DC power supply 112. A 450 MHz power supply 211 for plasma generation and a 13.56 MHz power supply 213 for antenna bias are connected to the antenna plate 205 via a filter 212 and two kinds of frequencies are applied to the antenna plate 205. The power supplies are connected to the filter 212 via matching apparatuses 214 and 215, respectively. A coaxial cable 204 and the antenna plate 205 are connected via a member of an almost conical shape, so that the high frequencies propagated via the coaxial cable 204 are efficiently transmitted to the antenna plate 205. Reference numeral 219 denotes a temperature controlling inner wall means provided on the inside of the chamber 104; 227 an annular member provided for the stage 108 and arranged on the outer peripheral part of the sample 107; 223 a power supply connected to the annular member 227 for controlling a plasma distribution; 224 a pass through which a heating medium for controlling the temperature of the stage 108 flows; and 220 a filter for an antenna bias, which will be described hereinlater, provided between the coaxial cable 204 and the ground potential.

[0077] In the etcher, when electromagnetic waves (microwaves) of 450 MHz for plasma generation are supplied to the antenna plate 205, the antenna plate 205 operates as a plane antenna. The ceiling (opposite to a plasma generating region) of the chamber 104 above the antenna plate 205 and the antenna plate 205 face each other and the ceiling is connected to an earth potential. Between the ceiling and the antenna plate 205, a dielectric 216 made of quartz, alumina, or the like is disposed. The diameter of the antenna plate 205, the material and thickness of the dielectric, and the like are determined so that the electromagnetic waves of 450 MHz resonate in a TM₀₁ mode between the ceiling and the antenna plate 205. The 450 MHz electromagnetic waves resonated by the plane antenna structure pass through the dielectric 216 and a ring made of a dielectric (called a quarts ring 217 since quartz is used here) arranged around the antenna plate 205 and are emitted into the plasma. A part of the electromagnetic waves propagates as a surface current on the surface of the antenna plate 205 and emits from a part contacting the plasma. In this manner, the electromagnetic waves of 450 MHz supplied to the antenna plate 205 are efficiently supplied via the dielectric 216 and the quartz ring 217 to the outer peripheral space part in the chamber 104, and are resonated with the magnetic field generated by the coils 105. Consequently, the plasma can be easily generated and maintained.

[0078] The antenna plate 205 is operated as a plane antenna plate and, according to the embodiment, the electromagnetic waves and the magnetic field are electronic cyclotron resonated. The magnetic field in this case has to be strong enough to bring about the electronic cyclotron resonation with the electromagnetic waves of 450 MHz and is 100 to 200 gauss. A magnetic field having such strength is generated by the coil 105. Since the electromagnetic waves can be efficiently supplied from the antenna plate even in a state where there is no magnetic field, the plasma can be generated. The etcher of this embodiment is not therefore limited to the case where the magnetic field is used.

[0079] The quartz ring 217 is arranged around the antenna plate 205. The quartz ring 217 has an effect on suppressing that the magnetic field around the antenna plate 205 or the plate 218 made of silicon for supplying an etching gas becomes locally strong, so that the plasma can be generated uniformly.

[0080] In case of using the electronic cyclotron resonance with the magnetic field, uniformity of the plasma and the magnetic field parameters have a close relation. An electronic cyclotron resonance region can be set at an arbitrary position by the coils 105 provided around the chamber 104. According to the embodiment, since the electromagnetic waves of 450 MHz are used, the resonance region is a region where the magnetic field of about 160 to 180 gauss is generated. Since the plasma is efficiently generated in the resonance region, the plasma density is high. The resonance region is, however, largely influenced by the magnetic field parameters. By regulating the position of the electronic cyclotron region, the magnetic field gradient (rate of change in the magnetic field strength), the shape of the resonance region, and the like so that the plasma density in the etching region is uniformized, setting adapted to each etching can be made.

[0081] The etcher of this type can also improve the verticality of the sidewall by on-off modulating the rf bias power supply 109 as described in the foregoing embodiment. The essence of the etcher of FIG. 18 is that the frequency band of the power supply 211 for plasma generation corresponds to the electromagnetic waves in the microwave region of so-called VHF to UHF bands from 100 MHz to 1 GHz. Additional functions which will be described hereinbelow are not always necessary. The power supply 213 for antenna bias of 13.56 MHz connected to the antenna plate 205 is to control chemical species in the plasma by applying a bias to the antenna plate 205 and is not always necessary. The circular member 222 around the stage 108 is provided to control the uniformity of the plasma and is not always necessary. A structure that the antenna plate 205 is disposed out of the chamber can be also employed.

[0082] An eighth embodiment of the invention characterized by a sample attracting method will now be described. As mentioned above, in the invention, in order to perform high-accuracy etching by on-off modulating the rf bias voltage at high speed, the rf bias has to be applied uniformly to the sample without causing distortion in waveform or the like. It is therefore necessary to attract the sample to the stage without a large gap. If there is a gap, ununiformity occurs in the application of the rf bias according to the electric capacity. In the on-off bias modulation, therefore, as shown in FIG. 1, the combination with the electrostatic chuck type stage is important. Since the rf bias is on-off modulated in the on-off bias modulation, there is the possibility that a fluctuation occurs in the electrostatic attraction. It is therefore preferable to combine with a dipole type electrostatic chuck which will be described hereinbelow.

[0083]FIG. 19 is an enlarged diagram of the stage part of the etcher as described above, having the dipole type electrostatic chuck structure. The stage 108 has a second electrode 301 as an electrode for electrostatic chucking surrounded by an insulating part 302. A DC voltage is applied to the stage 108 via a low pass filter 113. The sample 107 can be attached and detached to/from the stage 108 by a pusher 303 and a lifting mechanism 304. The stage having the monopole type electrostatic chuck apparatus shown in FIG. 1 cannot attract the sample when the plasma is not generated. The dipole type stage of the present embodiment can attract the sample without a plasma by applying a voltage of a different polarity to the stage 108 and the second electrode 301. The sample can be therefore attracted without being influenced by the on-off states of the rf bias, so that the stability is excellent.

[0084]FIG. 20 shows a ninth embodiment of the invention. In an etcher, the microwaves oscillated from the magnetron for generating a plasma is also on-off modulated. In the structure, a pulse modulator 401 is connected to the microwave power supply 101 and the plasma is on-off modulated by pulse waves 2001. By executing the on-off modulation to the plasma, the electron temperature decreases. Consequently, an effect that a damage to the sample by charged particles can be reduced is produced. A positive pulse 2002 can be also overlapped on the rf bias power supply 109 in the OFF period. By the operation, electrons are attracted to the fine pattern on the surface of the sample, thereby enabling a damage caused by charging to be suppressed.

[0085] As a tenth embodiment, other parameters of etching will be explained. The parameters described in the foregoing embodiments are typical values. Even when the pressure of etching gas, the kind of the etching gas, the value of a power for plasma generation, and the like are changed, the on-off bias modulation in the invention is effective. When the etch rate and the selectivity are taken into account, however, an application within the following range is desirable. With respect to the mixed gas of chlorine and oxygen used for etching mainly polysilicon and a multilayer including polysilicon, 0% to 50% of the mixing ratio of oxygen is proper when the flow of chlorine is 20 sccm to 1000 sccm. When the mixing amount of oxygen becomes larger than that, the etch rate of polysilicon becomes extremely low. 0.1 Pa to 10 Pa is proper for the pressure. In case of using the mixed gas of chlorine, HBr, and oxygen as an etching gas, when a flow of each of chlorine and HBr is 20 sccm to 1000 sccm, a proper mixing ratio of oxygen is 0% to 50%.

[0086] For etching of a metal conductive line made of Al or the like, chlorine, a mixed gas of chlorine and BCl₃, a mixed gas of chlorine and HCl, and a mixed gas of chlorine, BCl₃, and HCl are suitable. In this case, at a flow rate of each of chlorine and HCl of 20 sccm to 1000 sccm, a proper mixing ratio of BCl₃ is 0% to 50%. Further, a rare gas such as CH₄ or argon can be also mixed to each of the gasses.

[0087] The density of the plasma is determined by the power of the power supply for plasma generation and has a close relation with the etch rate. In order to obtain a practical rate, the power for the volume of a plasma generating space, that is, a space between the stage and the electrode is set to 0.01 W/cc or larger. When the plasma density is too high, a problem such as an electric damage to a device occurs. It is therefore preferable to set the power to 0.2 W/cc or smaller.

[0088] The frequency of the bias power supply to be applied to the sample is preferably 100 kHz to 100 MHz. Although the band of the ion energy can be narrowed with respect to a frequency higher than that, a problem that a plasma is easily generated by the bias power supply occurs. When the on-off frequency is 100 Hz or lower, the on/off time is too long and an etched sidewall becomes unsmooth. When the on-off frequency is high, it is technically difficult to produce the power supply. Consequently, the frequency lower than or equal to 10 kHz is suitable.

[0089] The invention produces a special effect on both a process of a fine pattern in which an interval between a line and a space is 0.5 μm or smaller, and a process of a sample in which the thickness of an underlying oxide film is 6 nm or smaller in a gate electrode.

[0090] According to the invention as described above, there are the following features.

[0091] By on-off modulating the rf bias voltage to which a Vpp value larger than the Vpp value of a continuous rf bias voltage at which the same etch rate can be obtained is given, the degree of anisotropy can be improved without deteriorating the selectivity.

[0092] By setting the frequency of the rf bias voltage to 15 MHz or lower and setting the Vpp value of the rf bias voltage to 500V or higher, the microtrench is reduced and the degree of anisotropy can be raised.

[0093] When the frequency of the rf bias voltage is higher than 15 MHz, by setting the Vpp value of the rf bias voltage to 800V or higher, the microtrench is reduced, and the degree of anisotropy can be increased.

[0094] By setting the duty when the rf bias voltage is “ON” to 5 to 50%, the effect of the improved selectivity can be made more conspicuous.

[0095] The sample surface treatment from the beginning till the end is divided into a plurality of steps and the rf bias voltage is on-off modulated in at least one of the steps, thereby enabling a region having high selectivity or a region having high anisotropy to be properly used. Thus, the processing accuracy can be further raised.

[0096] The plurality of steps are divided into the first half in which the etch rate of the underlying substance is relatively low and the latter half in which the etch rate is relatively high. By on-off modulating the rf bias voltage at least in the steps of the first half, the region in which the anisotropy is high can be effectively used in the on-off modulation and the etch profile can be improved.

[0097] The steps are switched according to time, thereby enabling etching of a complicated multilayer to be accurately performed by a simple switching control.

[0098] Independent of the plasma generation, the rf bias having the frequency of 100 kHz or higher is applied to the sample, and the rf bias is modulated at the frequency of 100 Hz to 10 kHz. In this manner, the surface treatment in which the minimum feature size is 1 μm or smaller is performed to the sample. Consequently, the ion energy band is narrowed, the effect of the on-off bias can be produced more effectively, and the finer etch can be carried out.

[0099] By using the high density plasma having the electron density of the plasma of 1×10¹⁰/cm⁻³ or higher, the etch having a high throughput can be carried out.

[0100] The etching having higher selectivity between polysilicon and the oxide film can be performed by using a mixed gas of chlorine and oxygen as an etching gas.

[0101] The surface of a sample is treated in such a manner that a plasma is generated from the etching gas by using the microwaves, independently of the plasma generation, the rf bias having the frequency of 100 kHz to 10 MHz is applied to the stage, the rf bias is on-off modulated at the frequency of 100 Hz to 10 kHz, and the Vpp value of the rf bias voltage at the time of “ON” is set to 100V or higher, thereby enabling the etching having a high selectivity to be performed with high throughput.

[0102] By employing an ECR plasma using microwaves of 2.45 GHz as the plasma, the magnetron can be used as a power supply. Thus, the above-described effects can be obtained while keeping the price of the etcher low.

[0103] By employing an ECR plasma using microwaves of 100 MHz to 1 GHz as the plasma, since the wavelength of the microwave is long, the above-mentioned effects can be obtained by using the uniform plasma having a larger diameter.

[0104] The sample having a pattern whose minimum feature size is 1 μm or smaller is held by electrostatic chucking, and the sample is treated with a plasma by time modulating the rf bias to be applied to the sample independently of the plasma generation. Consequently, the on-off modulated rf bias is uniformly and efficiently transmitted to the sample. Thus, a sample having a fine pattern can be treated with high accuracy and high reliability.

[0105] By holding the sample by the electrostatic chuck of the dipole type, some attraction can be obtained irrespective of on/off states of the rf bias, so that the reliability of the work is improved.

[0106] The sample having the film made of a material which serves as a gate electrode on the gate oxide film having the thickness of 6 nm or smaller is subjected to the plasma treatment by time modulating the rf bias applied independently of the plasma generation, thereby enabling the upper layer to be etched while sufficiently leaving the thin oxide film.

[0107] By applying the on-off modulation of the rf bias to a sample having a polysilicon film as a film serving as a gate electrode or having a multilayer including a polysilicon film, the highly anisotropic etching can be performed.

[0108] With respect to the on-off modulation of the rf bias in the foregoing embodiments, stopping of the application of the rf bias voltage in the rf bias off period, setting of the output of the rf bias voltage to 0V, and application of a voltage small enough to exert no influence on the effects of the rf bias off period are included in the on-off modulation of the rf bias voltage or time modulation of the present invention. 

What is claimed is:
 1. A method of treating a surface of a sample, comprising the steps of: generating a plasma in a treatment chamber; applying an rf bias voltage to a stage on which a sample is placed independently of the generation of the plasma; and on-off modulating an rf bias voltage to which a peak to peak voltage Vpp value larger than a Vpp value of a continuous rf bias voltage at which the same etch rate can be obtained is given.
 2. A method according to claim 1, wherein the frequency of the rf bias voltage is set to 15 MHz or lower and the Vpp value of the rf bias voltage is set to 500V or higher.
 3. A method according to claim 1, wherein the frequency of the rf bias voltage is set to be higher than 15 MHz and the Vpp value of the rf bias voltage is set to 800V or higher.
 4. A method according to claim 1, wherein a duty ratio when the rf bias voltage is in the on state is set to 5 to 50%.
 5. A method according to claim 1, wherein the sample surface treatment from the beginning till the end is divided into a plurality of steps and the rf bias voltage is on-off modulated in at least one of the steps.
 6. A method according to claim 5, wherein the plurality of steps are grouped into the first half in which a selectivity for a substance of an underlying film is relatively low and the latter half in which the selectivity is relatively high, and the rf bias voltage is on-off modulated at least in the steps of the first half.
 7. A method according to claim 6, wherein the steps are switched according to time.
 8. A method of treating a surface of a sample, comprising the steps of: arranging a sample on a stage provided in a chamber; continuously supplying an etching gas into the chamber and generating a plasma from the etching gas; applying an rf bias of a frequency of 100 kHz or higher to the stage independently of the generation of the plasma; and modulating the rf bias at a frequency of 100 Hz to 10 kHz to perform a surface treatment in which a minimum feature size is 1 μm or smaller to the sample.
 9. A method according to claim 8, wherein the plasma is a high-density plasma having an electron density of 1×10¹⁰/cm⁻³ or higher.
 10. A method according to claim 8, wherein the etching gas is a mixed gas of chlorine and oxygen.
 11. A method of treating a surface of a sample, comprising the steps of: arranging a sample on a stage provided in a chamber; continuously supplying an etching gas into the chamber and generating a plasma from the etching gas by using microwaves; applying an rf bias of a frequency of 100 kHz to 10 MHz to the stage independently of the generation of the plasma; on-off modulating the rf bias at a frequency of 100 Hz to 10 kHz; and a Vpp value of the rf bias voltage in the on state is set to 100V or higher and the surface of the sample is treated.
 12. A method according to claim 11, wherein the plasma is an ECR plasma using microwaves of 2.45 GHZ.
 13. A method according to claim 11, wherein the plasma is an ECR plasma using microwaves of 100 MHz to 1 GHz.
 14. A method of treating a surface of a sample, wherein when a sample having a pattern whose minimum feature size is 1 ?m or smaller held on a stage provided in a chamber by electrostatic chucking is etched with a plasma generated by continuously supplying an etching gas into the chamber, the sample is treated by applying an rf bias to the stage independently of the plasma generation and time modulating the rf bias.
 15. A method according to claim 14, wherein the electrostatic chuck of the sample is that of a dipole type.
 16. A method of treating a surface of a sample, wherein when a sample having a film made of a material serving as a gate electrode on a gate oxide film having the thickness of 6 nm or smaller is etched with a plasma, an rf bias is applied to the sample and is also time modulated.
 17. A method according to claim 16, wherein the film made of the material serving as the gate electrode is a polysilicon film or a multilayered film including a polysilicon film.
 18. A sample surface treating apparatus comprising: a stage which is provided in a chamber and on which a sample to be subjected to a surface treatment is placed; etching gas supplying means for continuously supplying an etching gas for plasma generation into the chamber; plasma generating means for generating a high-density plasma in the chamber; a bias power supply for applying a bias voltage of 100 kHz or higher to the stage independently of the plasma generation; and pulse modulating means for modulating the bias power supply at a frequency of 100 Hz to 10 kHz, wherein the surface treatment in which the minimum feature size is 1 μm or smaller is performed to the sample placed on the stage.
 19. An apparatus according to claim 18, wherein the amplitude of the rf voltage of 500V or higher can be generated when the frequency of the rf power supply is 15 MHz or lower, and the amplitude of the rf voltage of 800V or higher can be generated when the frequency of the rf power supply is higher than 15 MHZ.
 20. An apparatus according to claim 18, wherein the high-density plasma is generated by either an Electron Cyclotron Resonance system, or an Inductively Coupled Plasma system.
 21. A sample surface treating apparatus comprising: a stage which is provided in a chamber and on which a sample to be subjected to a surface treatment is placed; etching gas supplying means for continuously supplying an etching gas for plasma generation into the chamber; plasma generating means for generating a high-density plasma in the chamber by using microwaves; a bias power supply for applying a bias voltage of 100 kHz to 10 MHz to the stage independently of the plasma generation; and pulse modulating means for modulating the bias power supply at a frequency of 100 Hz to 10 kHz, wherein the amplitude of the rf voltage as the bias power supply is set to 100V or higher.
 22. An apparatus according to claim 21, wherein said plasma generating means uses electron cyclotron resonance by using microwaves whose frequency is 2.45 GHz.
 23. An apparatus according to claim 21, wherein said plasma generating means uses electron cyclotron resonance by using microwaves whose frequency is 100 MHz to 1 GHz. 